The present invention relates to a device for maintaining a constant temperature for chemical analysis. In particular, the invention relates to a device for maintaining a constant temperature for chemical analysis wherein a substance to be measured acts on a coloration reagent in a reagent layer of a multilayer chemical analysis film of a chemical analysis slide, the degree of coloration is measured or judged with a high accuracy using an optical system or the like, and the chemical analysis slide can be sealed and maintained at a constant temperature for a desired period of time.
In a test for determining, for example, the concentration of glucose or urea nitrogen in blood, the simplest conventional method is to use a test paper for coloration and to visually compare the degree of coloration of the test paper with a sample color density of a standard concentration of a substance which is to be measured. However, since the determination of the degree of coloration of the test paper depends upon the visual judgement of the human operator, this method is not satisfactory as far as its accuracy is concerned. Modern developments in medicine require a higher accuracy than can be obtained using this method.
There have been proposed various types of chemical analysis slides each having a multilayer chemical analysis film which is composed of at least two layers, specifically, a spreading layer and a reagent layer which is adapted for automatic analysis using an optical system. Using this slide, a predetermined amount of an aqueous sample solution containing a substance to be analyzed (analyte) is placed on the multilayer chemical analysis film of the chemical analysis slide. The slide is maintained at a constant temperature for a predetermined period of time after which it is irradiated with electromagnetic rays of a wavelength determined in accordance with the analyte and the reagent which is contained in the reagent layer of the multilayer chemical analysis film of the slide. Reflection or transmission optical density in a coloration area of the reagent layer is measured to obtain the concentration of the analyte. It should be noted that the transmission optical density measurement is carried out after layers or materials which prevent transmission of measuring rays have been removed.
Specific examples of the multilayer chemical analysis film are multilayer integral-type materials for analysis as described in Japanese Laid-Open Patent Application Nos. 53888/1974 (U.S. Pat. No. 3,992,158), 137192/1975 (U.S. Pat. No. 3,983,005), 40191/1976 (U.S. Pat. No. 4,042,335), 3488/1977 (U.S. Pat. No. Re. 30,267), 131786/1977 (U.S. Pat. No. 4,050,898), 142584/1977 (U.S. Pat. Nos. 4,053,381; 4,136,036; 4,050,451), 33651/1980 and 164356/1980. These multilayer chemical analysis films have a laminate film structure in which a reagent layer or layers and a porous spreading layer are formed integrally on a water-impenetrable support. If a constant amount of liquid as a test sample is dropped onto the outermost layer of the film, the liquid spreads to substantially a constant area and passes through the lower layer whereupon a reaction such as a coloration reaction takes place with the amount of coloration change being in proportion to the concentration of the analyte. By measuring the optical density of the coloration after a predetermined time, the concentration of the analyte in the liquid is colorimetrically determined. In this multilayer chemical analysis film, the outermost layer thereof is covered with a porous film of a type which substantially uniformly spreads the solution under test. Such a material is disclosed, for instance, in Japanese Laid-Open Patent Application No. 164356/1980 and U.S. Pat. No. 3,992,158.
In order to maintain a constant temperature of the multilayer chemical analysis film or the chemical analysis slide having the film, there has conventionally been used a device such as an incubator. Although conventional incubation may be capable of maintaining a constant temperature (37.degree. C. to 40.degree. C., for instance), using this device, the water component in the reagent layer which serves as a solvent or a dispersion medium in aqueous liquid samples tends to evaporate from the multilayer chemical analysis film thereby making it impossible to sufficiently accomplish reaction of the analyte and the reagent. Therefore, there is a tendency for the measured optical density of the coloration to be smaller than an actual optical density thereof. This results in an error in that the concentration of the analyte is erroneously determined, thereby making it impossible to obtain an analysis result with a desirably high accuracy.
In view of this drawback, it has been proposed to provide a cover for sealing the chemical analysis slide so that the multilayer chemical analysis film thereof is isolated from the outer atmosphere during the measurement operation. Using this technique, however, there are drawbacks in that the constitution of the slide, which can be used only once and then must be thrown away, becomes complex thereby increasing the manufacturing cost, rendering the temperature maintaining operation troublesome, and making it difficult to automate the analysis. Furthermore, the analyte can be easily contaminated.
Accordingly, an object of the present invention is to overcome the drawbacks accompanying the prior art devices as mentioned above by providing a device for maintaining a constant temperature during chemical analysis which has a simple construction and which is capable of actively preventing the evaporation of the water component from a multilayer chemical analysis film to which an aqueous liquid sample containing a substance to be measured (analyte) is applied as well as maintaining the quantity of water component and hence the concentration constant during the reaction period. Furthermore, it is desired to provide a device of this type in which the period of time for maintaining the constant temperature can be set as desired.